Lateral Diffused Metal-Oxide-Semiconductor (LDMOS) transistors formed by Bipolar, CMOS or DMOS (BCD) processes have been widely used in radio frequency power amplifiers (RF PAs) and microwave power amplifiers (MW PAs), etc. NLDMOS transistors refer to N-type LDMOS transistors.
An NLDMOS transistor includes a P-type body (P-body) region and an N-type drift (N-drift) region. An N-type heavily doped source region is disposed in the P-body region; and an N-type heavily doped drain region is disposed in the N-drift region. Further, an insulation structure is also disposed in the N-drift region; and the insulation structure is disposed between the N-type heavily doped source region and the N-type heavily doped drain region. Further, a gate oxide layer and a gate are sequentially formed over a portion of the P-body region and a portion of the insulation structure.
Usually, some other devices are also formed on and/or in the substrate of the NLDMOS transistors. If the carriers of the devices diffuse into the substrate having the N-type heavily doped source region and the N-type heavily doped drain region, or the carriers of the N-type heavily doped source region and the N-type heavily doped drain region diffuse into the devices, interferences between devices would occur; and the performance of the NLDMOS transistor may be affected. Therefore, to prevent the diffusions between the devices formed in the substrate, a deep P-type doped well (DPW) region and a deep N-type doped well (DNW) region are often sequentially formed from inside to outside to cover the P-body region and the N-drift region of the NLDMOS transistor. The DPW and the DNW are able to increase the carrier insulation performance of the NLDMOS transistor.
However, the production cost of the NLDMOS transistors having such structures is relatively high. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.